1. Field of the Invention
The present invention relates to a pillar structure of a vehicle, including a pillar member having a cross section open toward an inside of a compartment.
2. Description of the Related Art
A center pillar of an automobile is connected to a roof side member in an upper portion of a transversely outer vehicle body and a side sill in a lower portion of the vehicle body so as to stride over the vehicle body. On the center pillar, a door hinge of a rear door, a shoulder adjuster of a seat belt, and the like are attached. Accordingly, the center pillar generally has a structure with a closed cross section for strength required to support them.
The Japanese Patent application Laid-Open No. 2001-122155 discloses a pillar structure, in which the pillar member is formed into a structure with an open cross section by casting of a lightweight alloy such as aluminum for reducing weight thereof.
In addition to strength for supporting, the pillar member requires strength for restricting a bending deformation caused by a side collision or the like.
To restrict the bending deformation, it is necessary to increase a geometrical moment of inertia of the pillar member. However, due to limitations relative to the door, the outer size of the cross section of the pillar member is restricted, and the wall thickness of the entire pillar member is increased to gain the geometrical moment of inertia, thus increasing the weight thereof overall, even if an aluminum alloy is used for weight reduction.
It has been conceived that only an outer wall on an outside in a vehicle transverse direction, where a collision load to the pillar member is directly inputted in the event of side collision, be made thicker. However, in the case this is adopted to the pillar member with an open cross section, front and rear walls, respectively extended from front and rear ends of the outer wall of the pillar member, are more likely to deform, tilting in such a direction that the front and rear walls are opened, at an input of the collision load. The flexural rigidity thereof is thus lowered, and an amount of deformation is increased. Therefore, the wall thickness of the front and rear walls cannot be decreased, resulting in an increase in weight.
When the pillar member is cast from an aluminum alloy, molten metal is flowed from one of the front and rear walls through the outer wall to the other in a mold. In such a case, in terms of a casting ability, it is necessary to avoid such a shape of the pillar member that the wall thickness thereof sharply varies in a flow direction of the molten metal.
An object of the present invention is to provide a lightweight pillar structure for a vehicle with high flexural rigidity, without increasing thickness of the entire wall of the pillar member with an open cross section.
An aspect of the present invention is a pillar structure comprising: a pillar member connected to an upper potion and a lower portion of a transversely outer vehicle body, the pillar member being formed into a channel open toward a compartment, with a transversely outer base wall, and a pair of side walls thinner than the base wall, extending from both front and rear sides of the base wall, wherein each of the side walls is formed to have a first tapered portion gradually reducing in thickness from a base end portion of the side wall to a substantially center portion of the width thereof, and stiffening projections formed on an inner surface of the side wall at predetermined intervals in a pillar longitudinal direction, extending from a distal end portion of the side wall to the base end portion thereof.